The present invention relates to an image display device for displaying an image by modulating lights from backlights using, e.g., a liquid-crystal display panel, and a backlight device used for this image display device. More particularly, it relates to an image display device which is so configured as to divide an image display region into a plurality of regions, and to control the brightness of a backlight in each region, and a backlight device used for this image display device.
Basically speaking, image display devices can be classified into self-light-emitting-type image display devices such as CRT (: Cathode Ray Tube), and non-light-emitting-type image display devices such as liquid-crystal display (which is also referred to as “liquid-crystal display device” or “liquid-crystal display panel”).
As the non-light-emitting-type image display devices, there exist an image display device which uses a reflection-type light modulation element for adjusting the light's reflection light amount in accordance with an image signal, and an image display device which uses a translucence-type light modulation element for adjusting the light's translucence light amount in accordance with the image signal. In particular, the liquid-crystal display device uses the liquid-crystal display panel as the translucence-type light modulation element, and is equipped with an illumination device (which is also referred to as “backlight device”) on the rear surface of the display panel. Since the liquid-crystal display device is a thin-type and lightly-weighted display device, the liquid-crystal display device is employed as various kinds of display devices such as computer's monitor and television.
Here, basically speaking, the backlight schemes in the liquid-crystal display device are classified into the two schemes, i.e., the directly-below scheme and the edge-light scheme. The directly-below scheme is the following scheme: Namely, one or more fluorescent lamps or LEDs (: Light-Emitting Diodes), which become light-sources, are arranged directly below the liquid-crystal display panel. Meanwhile, the edge-light scheme is as follows: Namely, one or more fluorescent lamps or LEDs, which become light-sources, are deployed at an end portion (i.e., edge portion) of a plate-profiled light-guiding plate that is formed using, e.g., an acryl plate. Moreover, the light-sources are converted into a surface light-source by taking advantage of the multiple reflection inside the light-guiding plate.
By the way, in the self-light-emitting-type image display devices the representative of which is the CRT, when displaying an image, a particular pixel is selectively caused to emit light in a necessary light amount in accordance with an image signal. Also, in an aspect of the picture-quality, from the relationship of a distance with the deflection center of an electron beam used in the image display devices, the luminance of the standard field-of-view (whose horizontal angle: ±15°, uppermost angle: 8°, and lowermost angle: 12°), i.e., the standard visual angle of the NTSC (: National Television System Committee) television scheme, is made relatively higher as compared with the luminance of a screen's peripheral portion from the screen's center. Here, if the luminance outside the standard field-of-view is equivalent to or is higher than the luminance inside the standard field-of-view, humans feel a sense of strangeness on their sense of sight. Based on this fact, in the range of a sense-of-sight-range's effective field-of-view that humans possess, it has become possible to implement an image display where there occurs none of the sense of strangeness on the humans' sense of sight.
In contrast to this situation of the self-light-emitting-type image display devices, in the non-light-emitting-type image display devices such as, in general, the liquid-crystal display device, the backlights are caused to emit lights in such a manner that a constant brightness of each backlight is always maintained regardless of the image signal. Accordingly, the backlights are usually caused to emit the lights so that the brightness (which is also referred to as “luminance”) of the screen becomes equal to its maximum value. This fact gives rise to the occurrence of the virtual sense of strangeness on the humans' sense of sight. As a result, when the liquid-crystal display device is compared with the CRT, a little unsatisfactoriness has remained in the aspect of the picture-quality.
In order to address the above-described problem, from conventionally, the proposal has been made concerning the following liquid-crystal display device: Namely, by controlling the brightness of each backlight, this liquid-crystal display device makes it possible to implement the image display where, in the range of the sense-of-sight-range's effective field-of-view that humans possess, there occurs none of the sense of strangeness on the humans' sense of sight. Conventionally, as this type of technology, there has been known a technology disclosed in, e.g., JP-A-4073435, the counterpart US Publication of which is US 2006/0139952.
This technology disclosed in JP-B-4073435 is as follows: Namely, in the directly-below-scheme backlights where the LEDs are used as the light-sources, as illustrated in, e.g., FIG. 14, the backlights are divided into a plurality of regions (i.e., region 1 to region 4) in a substantially concentric manner from the screen center. Furthermore, the luminances of the light-sources are controlled for each region divided. This control method makes it possible to reduce the consumption power, while implementing the image display where there occurs none of the sense of strangeness on the humans' sense of sight.